This invention relates to molding compositions and particularly to molding compositions that cure during thermal treatment and which can nevertheless be thermoformed.
For most molding compositions based on thermoplastic polymers, the shaping operation does not involve any radical change in molecular structure, that is to say, it remains thermoplastic. The consequence of this thermoplastic character is that the mechanical properties such as modulus will decrease with increasing temperature and the polymer will usually have a low resistance to organic solvent such as might be used as paint vehicles for example.
If a thermosetting resin is chosen, the solvent and modulus deficiencies are considerably reduced but the resin cannot be thermoformed by conventional thermoplastic fabrication techniques. Furthermore, high modulus thermosetting resins all suffer from a lack of toughness which precludes their use in many applications. By contrast the polymers of the invention not only have good solvent resistance and high modulus but have in addition an unexpectedly high toughness.
The polymer compositions of the invention therefore, provide many of the advantages of both thermoplastic and thermosetting resins in that the polymers are tough and a broad range of thermoplastic forming operations can be used and the thermoformed polymer can be given good solvent resistance and retention of modulus by appropriate selection of reaction conditions.
The polymer is believed to acquire these properties through crosslinking and the amount that occurs can be controlled by variation of the composition of the polymer and the heat history of the polymer during processing.
The polymer of the invention thus provides a hybrid between true thermoplastic and thermosetting polymers that has many of the better characteristics of both.